Two-dimensional code

ABSTRACT

Disclosed is a two-dimensional code which is not likely to be affected by contamination or out-of-focus photographing thereof and can thus be accurately recognized even when it is photographed under various photographing conditions. The disclosed two-dimensional code comprises: cells representing binary-coded data that are arranged as a pattern in the form of a two-dimensional matrix, the two-dimensional code comprising: a position detection pattern; plural data blocks created by dividing a region of the two-dimensional matrix that excludes the part of the position detection pattern; and a separation space arranged between the plural data blocks that are adjacent.

FIELD OF THE INVENTION

The present invention relates to a two-dimensional code.

DESCRIPTION OF THE RELATED ART

Compared to one-dimensional codes, two-dimensional codes are capable ofstoring more information in a smaller area and are thus widely utilizedin a variety of applications, including inventory management and Webderivatives using mobile phones. Since two-dimensional codes arephotographed (taken) at various angles, the sizes and the orientationsof their images projected on a screen are not constant, and distortion,blurriness and the like of the images may occur. Further, when atwo-dimensional code is dirty, a part of its image may not berecognized.

In conventional two-dimensional codes, great importance was attached tothe data efficiency and this consequently made the two-dimensional codeslikely to be adversely affected by contamination, out-of-focusphotographing and the like. For example, in a case where an inventory ismade using a plurality of two-dimensional codes projected on a singlescreen, it is difficult to bring all of the two-dimensional codes intofocus when taking an image thereof, and an out-of-focus image is thuslikely to be produced. Since it is difficult to correct an out-of-focusor blur image of a two-dimensional code and an improvement by softwareis thus limited, an improvement of hardware, such as an improvement ofthe auto-focus function and an increase in the shutter speed, isrequired, and this leads to a problem of an increased cost. Recently,there is a need for a two-dimensional code to be recognized by camerasmounted on mobile phones; however, because such cameras are used in anenvironment that is likely to create problems for the analysis of atwo-dimensional code, such as image blurriness caused by tilting,movement or insufficient focusing of the cameras during photographing,and also from the standpoint of their cost and size, it is difficult toimprove the mobile phone cameras and the like at present.

PRIOR ART REFERENCES Patent Documents

[Patent Document 1] Japanese Laid-open Patent Publication No. H7-254037

[Patent Document 2] Japanese Laid-open Patent Publication No.2004-234318

[Patent Document 3] Japanese Laid-open Patent Publication No.2007-241328

[Patent Document 4] Japanese Laid-open Patent Publication No.2009-163720

[Patent Document 5] Japanese Laid-open Patent Publication No.2009-075873

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

There have been used and proposed a variety of two-dimensional codes;however, there is still a demand for a two-dimensional code which can beaccurately recognized in a short time even when it is photographed undervarious conditions.

An object of the present invention is to realize a two-dimensional codewhich is not likely to be affected by contamination thereof,out-of-focus photographing or the like and can be accurately recognizedin a short time even when it is photographed under various photographingconditions.

Means for Solving the Problems

In order to achieve the above-described object, the two-dimensional codeof the present invention is a two-dimensional code comprising cellsrepresenting binary-coded data that are arranged as a pattern on atwo-dimensional matrix, the two-dimensional code being characterized bycomprising: a position detection pattern; plural data blocks created bydividing a region of the two-dimensional matrix that excludes the partof the position detection pattern; and a separation space arrangedbetween adjacent plural data blocks.

Therefore, the accuracy of light-dark determination of cells in eachdata block is improved.

It is desired that the plural data blocks comprise a format informationblock indicating which of plural expressions is represented by the datablocks.

Therefore, the data capacity and redundancy of the two-dimensional codecan be set as appropriate in accordance with the intended use and useenvironment of the two-dimensional code.

One of the plural expressions is 7-bit expression in which eight cellsother than the central cell are fixed to contain four light cells andfour dark cells, the 7-bit expression representing 140 patterns.

The other of the plural expressions is 6-bit expression in which eightcells other than the central cell are fixed to contain four light cellsand four dark cells and the central cell is fixed to be light or dark,the 6-bit expression representing 70 patterns.

It is desired that the position detection pattern has an area largerthan the data block.

Further, it is also desired that the data blocks each have a size of 3×3cells, that the separation space have a width of one or more cells, andthat the position detection pattern has a lateral width of four or morecells and a vertical length of four or more cells.

Therefore, the accuracy of detecting the position detection patterns isimproved.

A method of analyzing a two-dimensional code comprising plural datablocks that contain format an information block comprises: identifying aposition detection pattern; calculating the position of the formatinformation block based on the thus identified position detectionpattern; analyzing the format information block; determining which ofplural expressions is represented by the data blocks; and performing ananalysis in accordance with the thus determined expression of the datablocks.

Further, a system for generating the above-described two-dimensionalcode comprises: a position detection pattern-arranging means forarranging the position detection pattern at prescribed positions of atwo-dimensional matrix; a dividing means for dividing a region of thetwo-dimensional matrix outside the regions where the position detectionpattern is arranged into plural blocks between which a separation spaceis arranged; an information block-arranging means for selecting, fromthe plural data blocks, information block in which information requiredfor analysis of the two-dimensional code is arranged; and a messagedata-arranging means for adding a message header to each message to berecorded and sequentially arranging recorded data, in which an endmessage header is added to the tail of each message, in a region of thetwo-dimensional matrix outside the regions of the position detectionpattern and the information block.

Effects of the Invention

By using the two-dimensional code of the present invention, even aphotographed image of the two-dimensional code on which variousdeteriorations have occurred can be accurately analyzed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the two-dimensional code described in Patent Document1.

FIG. 2 illustrates a two-dimensional code according to the firstembodiment.

FIG. 3 illustrates the arrangement of plural blocks in thetwo-dimensional code of the first embodiment.

FIG. 4 illustrates pattern examples in which cells are designed to belight or dark according to their respective data in a two-dimensionalcode having a separation space and in a two-dimensional code without aseparation space.

FIG. 5 illustrates the types of data blocks used in the firstembodiment.

FIG. 6 illustrates 20-pattern-expression data type.

FIG. 7 illustrates an example of a two-dimensional code generated inaccordance with the two-dimensional code of the first embodiment.

FIG. 8 illustrates another example of a two-dimensional code generatedin accordance with the two-dimensional code of the first embodiment.

FIG. 9 illustrates a two-dimensional code according to the secondembodiment.

FIG. 10 illustrates an example of a two-dimensional code generated inaccordance with the two-dimensional code of the second embodiment.

FIG. 11 illustrates modification examples in which the positiondetection patterns of the two-dimensional code of the second embodimentare applied as two-dimensional patterns of different sizes and shapes.

FIG. 12 illustrates four position detection patterns of eachmodification example.

FIG. 13 illustrates a hardware configuration of a system for generatingand providing a two-dimensional code upon a request.

FIG. 14 is a flow chart illustrating the procedures of an encodingprocess in which a user accesses system hardware via user hardware andgenerates a desired two-dimensional code.

FIG. 15 is a flow chart illustrating the procedures of an encodingprocess in which a user accesses system hardware via a user hardware andgenerates a desired two-dimensional code.

FIG. 16 is a flow chart illustrating the procedures of an encodingprocess in which a user accesses system hardware via a user hardware andgenerates a desired two-dimensional code.

FIG. 17 illustrates a hardware configuration of a two-dimensional codeanalyzer which reads out and analyzes the two-dimensional code of thefirst embodiment.

FIG. 18 is a flow chart illustrating the procedures of a decodingprocess in which two-dimensional codes photographed by a user areanalyzed.

FIG. 19 is a flow chart illustrating the procedures of a decodingprocess in which two-dimensional codes photographed by a user areanalyzed.

FIG. 20 is a flow chart illustrating the procedures of a decodingprocess in which two-dimensional codes photographed by a user areanalyzed.

FIG. 21 illustrates checking the shapes of candidate position detectionpatterns.

MODE FOR CARRYING OUT THE INVENTION

Before describing the embodiments of the present invention, a generaltwo-dimensional code widely used at present will be described.

FIG. 1 illustrates the two-dimensional code described in Patent Document1.

As illustrate in FIG. 1, a two-dimensional code 1 comprises; threeposition detection patterns (positioning symbols) 2, which are arrangedat three corners; and a data region 3. The data region 3 corresponds toa part of the two-dimensional code 1 region that excludes the threeposition detection patterns 2 and their surrounding spacer parts. Eachposition detection pattern 2 comprises: dark parts, which are a squareframe 2 a and a square 2 c arranged inside the square frame 2 a; and alight part between the frame 2 a and the square 2 c, which is a squareframe 2 b. When a scanning line passes through the center of aphotographed image of the position detection pattern 2, the positiondetection pattern 2 yields a length ratio (frequency component ratio) ofdark:light:dark:light:dark=1:1:3:1:1, regardless of the direction of thescanning line. Accordingly, regardless of the rotational orientation ofthe two-dimensional code, a specific frequency component ratio of theposition detection pattern 2 can be detected only by a scanningoperation in a certain direction. Thus, the center of the positiondetection pattern 2 can be easily detected.

The data region 3 comprises bits that are densely arranged in a matrixform, and the bit matrix is divided into: alignment patterns (timingcells) 4, which are used for correction of the positions of the dotswithin the data region; format information of the two-dimensional codeand its error correction signals; version information and its errorcorrection signals; and data part. The alignment patterns 4, the formatinformation of the two-dimensional code and its error correctionsignals, and the version information and its error correction signalsare arranged at prescribed positions on the bit matrix of the coderegion 3. The remaining part is the data part where coded data arerecorded, and the part left after recoding the necessary data iscomposed of remainder bits. The data bits to be recorded aredistinguished from the remainder bits by an end pattern placed at theend of the data bits. The remainder bits, which are referred to as“padding”, are a string of light (“1”) bits; however, upon beingrecorded, they are generally subjected to a prescribed processing to beconverted into a string of light and dark bits.

The alignment patterns 4 is a string of light and dark bits (dots) usedfor correction of the positions of the dots within the data region and,as illustrated in FIG. 1, a plurality of the alignment patterns 4 arearranged. The alignment patterns 4 are different from the positiondetection patterns 2 which detect the reference position of the entiretwo-dimensional pattern.

In Patent Documents 3 and 4, it is described that bits of the dataregion 3, which are padding, are utilized to provide a bit image.

Embodiments of the present invention will now be described.

FIG. 2 illustrates a two-dimensional code according to the firstembodiment.

The two-dimensional code of the first embodiment has a size of 35×35cells and is divided into 9×9 blocks, with a one-cell light separationspace 23 being arranged between adjacent blocks. Accordingly, theseparation space is an 8×8, one-cell-width lattice pattern having gridsat block-size intervals. A first position detection pattern 12A isarranged in the part of the lower right 3×3 block and 3×3 separationspace; a second position detection pattern 12D is arranged in the partof the upper left 2×2 block and 2×2 separation space; a third positiondetection pattern 12B is arranged in the part of the upper right 3(lateral)×2 (vertical) block and 3×2 separation space; and a fourthposition detection pattern 12C is arranged in the part of the lower left2 (lateral)×3 (vertical) block and 2×3 separation space. Accordingly, inthe two-dimensional code, no pattern other than the first to the fourthposition detection patterns appear in the blocks, except in those wherethe first to the fourth position detection patterns are arranged.

The minimum unit of a code part of a two-dimensional code is a cell.Two-dimensional codes usually take a square or rectangular shape. Atwo-dimensional code can also take other shape; however, two-dimensionalcodes are mostly tetragonal, and the two-dimensional code of the firstembodiment also has a square shape. The shape of the two-dimensionalcode of the first embodiment is not restricted thereto and may berectangular or another shape.

Generally, two-dimensional codes represent data with light and darkcells, and the code part of the two-dimensional code of the firstembodiment also represents data with light and dark cells. There havebeen proposed two-dimensional codes whose cells are distinguished bycolor, such as the one described in Patent Document 2, as well as mirror(laterally reversed)-type two-dimensional codes. The present inventioncan be applied to such two-dimensional codes; however, in these cases aswell, as described below, the two-dimensional codes comprise four ormore position detection patterns of different forms.

The two-dimensional code of the first embodiment is a square of 35×35cells; however, the size thereof can be increased, or thetwo-dimensional code can have a shape with different vertical andlateral sizes, such as a rectangular shape. A 35×35-cell squaretwo-dimensional code is referred to as “version 2×2”. The smallestversion is “1×1”, which has a cell size of 27×27. It is defined herethat a design can be embedded when the vertical and lateral versions areboth 2 or higher. The reason why such a restriction of not embedding adesign into a code of version 1×1 is implemented is because embedding ofa design despite the small data capacity of the code further reduces thedata capacity and recognition of the code would consequently yieldhardly any data. The two-dimensional code of the first embodiment can beextended in each of the vertical and lateral directions. When thelateral version is 2 and the vertical version is 3, the code is denotedas “version 2×3”. An increase in the version by 1 corresponds to anincrease in the cell size by 8 and an increase in the block number by 2.Accordingly, a code of version 3×4 has a cell size of 43×51. The versioncan be selected to be, but not limited to, 1 to 20.

The first position detection pattern 12A has dark cell parts composed ofa single-cell-width square frame of 8×8 cells in size and a 2×2 squarein the center of the square frame. The second position detection pattern12D has a dark cell part of a single-cell-width square frame of 4×4cells in size. The third position detection pattern 12B has a dark cellpart of a single-cell-width laterally-elongated rectangular frame of 8×4cells in size. The fourth position detection pattern 12C has a dark cellpart of a single-cell-width vertically-elongated rectangular frame of4×8 cells in size.

In the first embodiment, the four different position detection patternsare each arranged at the four corners of the square two-dimensionalcode. The phrase “different position detection patterns” means that theposition detection patterns are different in terms of shape, size andarrangement orientation on the two-dimensional code, and also includecases where the position detection patterns have different line widthratios. However, since color is affected by the photographing conditionsand the like, color is not included as a subject of the difference, anda difference in a light-dark binary image is considered.

In the first embodiment, the position detection patterns are arranged inthe vicinity of each apex of the square or rectangle. This is because,as compared to a case where the position detection patterns are arrangedin one spot, the effects of contamination can be more dispersed byarranging them as far as possible from each other. However, thearrangement positions of the position detection patterns are notrestricted to the four corners. As in the first embodiment, by using notonly square position detection patterns but also rectangular ones, theirshapes, tilt angles and sizes can be easily distinguished, so that theposition detection patterns can be quickly recognized. In addition,since hollow rectangles are easily distinguished from other projectedimages, the data loss is small.

As for the reason why the four position detection patterns are arranged,in two-dimensional projective transformation used for calculating themapping of the data coordinate with high accuracy in analysis, in orderto calculate the coordinate of the code cells and photographed imagecorresponding to the cells, it is required that a set of four coordinatebe provided as a parameter. Even when only two or three positiondetection patterns are arranged, projective transformation can becarried out by calculating four points with interpolation of coordinate;however, since precise coordinate are not likely to be obtained due totilted image capturing, image distortion, blurriness and the like andthis greatly affects the accuracy of data extraction, four positiondetection patterns are arranged in the first embodiment.

Further, the reason why the position detection patterns are differentfrom each other is because, even if a position detection pattern werenot recognized, the unrecognized position detection pattern can besurely identified, and this enables estimation the coordinates of theunrecognized position detection pattern and, hence, correction of theposition detection pattern. When all the same position detectionpatterns are used, the identification of an unrecognized positiondetection pattern is not as easy as in a case of using positiondetection patterns that are all different, and correction of theposition detection pattern is thus difficult.

In the two-dimensional code, 56 blocks other than those of the fourposition detection patterns constitute the data region, comprising:actual data blocks; error correction code blocks; version informationblocks; format information blocks; and design-embedding informationblocks.

As described above, each block of the data region is constituted by 3×3cells and data is embedded block by block. The data region comprises:version information blocks 15 and 16; format information blocks 17; anddesign-embedding information blocks 18A, 18B, 19A and 19B, with theremaining blocks being actual data blocks 22. As described below, in thefirst embodiment, some of the actual data blocks 22 are utilized forerror-correcting codes and position correction patterns.

Accordingly, the blocks 22, remaining after excluding therefrom theposition detection patterns, version information blocks, formatinformation blocks, design-embedding information blocks, blocks in whicha position correction pattern is arranged and error correction codeblocks, are the actual data blocks. When a design is embedded, adesign-embedded block(s) indicated by the design-embedding informationblocks is/are also excluded from the actual data blocks. In the blocksbelonging to the actual data blocks, the actual data are recorded insuch a manner that the actual data are sequentially filled from theupper left to the right side and, once a row of blocks are filled, theactual data are then filled into the next lower row of blockssequentially from the left.

The blocks each have a size of 3×3 cells with each cell representing onelight or dark bit, and each block thus stores a maximum of 9-bitinformation (9-bit expression). In order to improve the tolerance toimage blurriness and fuzziness, the data capacity per block can be setto be smaller than 9 bits. In the first embodiment, the blocks were setto have a size of 3×3 cells; however, the block size is not restrictedthereto. The blocks can also have a size of 1×1 cell, which is theminimum size, or a size in which, for example, the vertical and lateralcell sizes are different.

The version information blocks record information on the size of thetwo-dimensional code. There are two types thereof, which are verticalversion information blocks 15 and lateral version information blocks 16,and each of them records the corresponding version information. Byarranging two vertical version information blocks 15 and two lateralversion information blocks 16, each type of which blocks records thesame information, at two distant spots, the risk of a defect caused bycontamination or the like is dispersed. As version information, blocksrepresenting a numerical version number (from 1 to 20 for each of thevertical and lateral directions) are arranged.

Each format information block 17 records format information composed ofa design-embedding flag (1 bit) and data-block-type data (2 bits), andthree format information blocks 17 all storing the same information arearranged at three spots. The design-embedding flag indicates thepresence or absence of an embedded design, i.e., whether or not adesign-embedding region is arranged. When a design is embedded,design-embedding information blocks are arranged. The data-block-typedata indicates the type of the data blocks, which means the datacapacity per block and is selected to be 6, 7 or 9 bits/block. The datacapacity decreases in the order of 9-bit, 7-bit and 6-bit expressions (9bits>7 bits>6 bits); however, the data can be more easily read out inthe order of 6 bits>7 bits>9 bits. The type of the data blocks is thusselected taking into consideration the level of image blurriness andfuzziness as well as the data capacity. This point will be describedlater.

A design is embedded block by block and, when a plurality of adjacentblocks constitute a design-embedding region, the separation spacesbetween the blocks are also included in the design-embedding region. Thedesign to be embedded has a tetragonal external shape, and the imagethereof may be any image, without being restricted to a cell-resolutionbinary image. Further, a plurality of tetragonal blocks may be providedfor embedding a design therein. For example, the design may be amulti-valued image having a higher resolution than the cells or a colorimage, or the design may be, of course, a cell-resolution binary image.In the first embodiment, as a restriction on embedding of a design, itis prescribed that no design be embedded into the two upper block rows,two left block columns, three lower block rows and three right blockcolumns of the code. In these areas outside the design-embedding region,depending on the specification of the two-dimensional code,design-embedding information blocks having image information arearranged.

The design-embedding information blocks record information pertaining tothe size of the region where a design is embedded as well as thepositions of the blocks therefore in either the vertical or lateraldirection.

There are two types of design-embedding information blocks, which arevertical-embedding information blocks 18A and 18B and lateral-embeddinginformation blocks 19A and 19B, and each of them records thecorresponding version information. The vertical-embedding informationblocks 18A and 18B record the height of the embedded design (3 bits or 6bits) and the offset height of the embedded design (3 bits or 6 bits).The lateral-embedding information blocks 19A and 19B specify the widthof the embedded design (3 bits or 6 bits) and the offset width of theembedded design (3 bits or 6 bits). Whether 3-bit information or 6-bitinformation is recorded depends on the version information as describedbelow. When the version is 2 to 4, 3-bit information is required; whenthe version is 5 to 20, 6-bit information is required; and when theversion is 2 to 4, the vertical-embedding information block 18B andlateral-embedding information block 19B are not necessary.

The design-embedding information blocks exist only when adesign-embedding flag is waved in a format information block. The firstembodiment assumes a case where only one design is embedded. When it isassumed to embed plural designs into plural regions, the bit number ofthe design-embedding flag is increased in the format information blockso as to indicate the number of design-embedding regions and, at thesame time, the design-embedding information block is arranged as many asthe number of the designs. The size and offset of each design arespecified at a block level. The block coordinates are expressed as “(n,m)” with the block in the upper left corner being the origin, and thenumber of lateral blocks and that of vertical blocks are expressed as“blW” and “blH”, respectively. In the first embodiment, thedesign-embedding region is restricted to a rectangular region formed byan upper left corner (2, 2) and a lower right corner (blW-4, blH-4).Accordingly, the maximum number of lateral blocks of a design is blW-5and the maximum number of vertical blocks of a design is blH-5.

With regard to the position of a design, by embedding the information onthe block coordinates of the starting point (upper left) and the blocksize into the code as design-embedding information blocks, the positionof the embedded design can be recognized when the code is analyzed. Inthe same manner as in the case of the version information blocks, thelateral and vertical information blocks are handled separately.Different data capacities are assigned between cases where blW-5 is lessthan 8 (lateral version of 2 to 4) and other cases (lateral version of 5to 20), and the vertical information blocks are handled in the samemanner. The values of blW and blH are determined by analyzing thelateral and vertical versions, respectively.

When the value of blW is less than 13, the lateral block size has aminimum of 1 block and a maximum of 8 blocks, and these 8 block sizescan all be represented by 3 bits. In the same manner, the number of thelateral offset blocks has 7 possibilities, which are 2 to 8, and these 7numbers can also be represented by 3 bits; therefore, the total datacapacity is 6 bits. Accordingly, these lateral block data arerepresented by 6 bits, which can be expressed using a single block. Thesame also applies to the vertical blocks. Meanwhile, when the value ofblW is 13 or larger, the lateral block size is represented by 6 bitsand, in the same manner, the number of the lateral offset blocks is alsorepresented by 3 bits. Accordingly, these lateral block data areexpressed using two blocks. The same also applies to the verticalblocks.

The lateral-embedding information blocks 19A and 19B are both arrangedoutside (in the upper and lower sides of) the upper-left and lower-rightlateral version information blocks, and the vertical-embeddinginformation blocks 18A and 18B are arranged outside (in the left andright sides of) the lower-left and lower-right vertical versioninformation blocks.

When no design is embedded, i.e. when the design-embedding flag of theformat information block indicates “null”, the design-embeddinginformation blocks and the region for embedding a design are no longernecessary, making the code efficient.

The position correction patterns are used for the purpose of correctingthe coordinate of the actual data blocks and error correction codeblocks, as well as the coordinate of the design-embedding informationblocks when a design is embedded. In the two-dimensional code, thesecoordinate can be approximately obtained from the position detectionpatterns; however, since errors occur in the coordinate of the dataregion due to twisting or bending of the paper, distortion of the lensor displacement during acquisition of the position detection patterns,the position correction patterns are arranged for correcting sucherrors. The position correction patterns are different from the positiondetection patterns in that they do not have to be distinguished fromother noises, and the positions of the position correction patterns areeasily determined as long as the position detection patterns can becalculated. Therefore, it is desired that the position correctionpatterns have such a form that enables fine coordinates corrections.

In the first embodiment, as position correction patterns, blockscomposed of a combination of predetermined cells (position correctionblocks) are arranged at regular intervals in place of actual data. If ablock coordinates (7n, 7m) (wherein, n and m are each an integer of 0 orlarger) is in the data region, a block in which a dark central cell issurrounded by light cells is arranged at the coordinates. However,should a position detection block, a version information block, a formatinformation block, a design-embedding information block or a designexist at the coordinates, no position correction block is arranged.Here, the block coordinates are expressed by defining the coordinates ofthe upper-left block as the reference coordinates (0, 0), with thecoordinates of the adjacent block on the right being (1, 0). It is notedhere that the block in which the position correction patterns arearranged is not restricted to the above-described one.

As the actual data, segments each composed of a combination of a messageand a header modifying the message (message type (message encode)message size) are arranged as many as the number of the messages. Inaddition, as a special segment, a segment which contains only an endflag without any message is generated and, when a capacity of the actualdata is left unused, this end-flag segment is arranged, followed bypadding. The actual data are divided into block units in accordance withthe data capacity per block which is indicated by the data-block-typedata. In the same manner, the error-correcting codes are also dividedinto block units.

When Reed-Solomon codes are used as the error-correcting codes, sincethe error corrections are performed word by word, it is desired that oneword constitutes one block. When one word spans over a plurality ofblocks, even if only one of the blocks is contaminated, all of the wordsassociated with the block are subjected to the error correction, whichimpairs the correction efficiency. Contamination and spotlight-causedcolor fading that lead to corrections are often concentrated in onespot. The division of the actual data into blocks has an effect ofputting together the data to be simultaneously corrected into one spot,and this enables efficient corrections and improves the probability ofthe code to be recognized.

As described above, the two-dimensional code of the first embodimentcomprises the separation space 23 of a single cell in width, which isarranged between the blocks. Therefore, the position detection patternsand the blocks are all surrounded by light cells.

FIG. 3 illustrates the arrangement of plural blocks in thetwo-dimensional code of the first embodiment. Each block has a size of3×3 cells, and the peripheries of the blocks are separated by theseparation space 23 of a single cell in width.

FIG. 4 illustrates pattern examples in which cells are designed to belight or dark according to their respective data in a two-dimensionalcode having the separation space 23 and in a two-dimensional codewithout the separation space 23. FIG. 4(A) illustrates a two-dimensionalcode comprising the separation space 23 and four blocks of 3×3 cells insize, wherein three of the blocks are patterns in which cells that arepositioned in the center and at four corners are dark and other cellsare light and one of the blocks is a pattern in which the light and darkcells of the other three blocks are reversed, and FIG. 4(B) illustratesthe two-dimensional code of FIG. 4(A) without the separation space 23.As illustrated in FIG. 4(B), without the separation space 23, theboundaries between the blocks are unclear and the light cells surroundedby dark cells may be blackened out.

As compared to the two-dimensional code without the separation space 23,the two-dimensional code having the separation space 23 is larger andthus has a lower data efficiency; however, since it is not likely to beaffected by the patterns of the adjacent blocks even when itsphotographed image is out-of-focus or blur, the accuracy of light-darkdetermination of each cell is improved. In fact, when an image of thetwo-dimensional code having the separation space 23 and that of thetwo-dimensional code without the separation space 23 are both subjectedto binarization, blackening-out of cells is more likely to occur in thelatter image. When the photographed image is out-of-focus or blur, thecells are each affected by the color of the surrounding cells. In FIG.4(B), whether a surrounding cell of a given cell is light or dark issubstantially random. Those cells surrounded by cells with largelydifferent colors are greatly affected and vice versa, and suchnon-uniformity of the effects of the surrounding cells makes colordetermination difficult. Explaining the cells constituting a block byassigning them with letters “a” to “i” as illustrated in FIG. 3, becausethe two-dimensional code of FIG. 4(A) has the separation space 23, thecells a, c, g and i are in contact with the separation space at five ofthe eight peripheral spots and the cells b, d, f and h are in contactwith the separation space at three of the eight peripheral spots. Thus,it can be said that the cells other than the cell e are less likely tobe affected by their surrounding cells as compared to the case of FIG.4(B). In addition, by allowing each block to have 6-bit expression asdescribed below, cell e, which is likely to be affected, is no longerevaluated and, since the cells a, c, g and i are now in contact with alight cell at six of the eight peripheral spots and the cells b, d, fand h are in contact with the a light cell at four of the eightperipheral spots, it can be said that the cells are further less likelyto be affected by image blurriness or fuzziness.

In this manner, by arranging the separation space 23, the risk that thecells may not be properly recognized due to blurriness or fuzziness canbe reduced.

As for the position detection patterns, even the smallest secondposition detection pattern 12D is a square of 4×4 cell in size and theblocks of 3×3 cells in size are separated by the separation space 23, apattern identical to any of the position detection patterns does notappear in the data block. Therefore, by arranging the separation space23, the detection process of the position detection patterns can beeasily carried out.

In the first embodiment, the data capacity per block can be selectedseparately for each type in accordance with the resistance to datadeterioration.

FIG. 5 illustrates the types of data blocks used in the firstembodiment.

FIG. 5(A) illustrates a data type in which bits “a” to “i” are assignedto each of 3×3 cells of a block so that 9 bits can be expressed. In thiscase, one block has an information capacity of 9 bits and is capable ofexpressing a value up to 2⁹=0 to 511.

When analyzing the data type of FIG. 5(A), for a binary image generatedfrom an input photographed image, the coordinate corresponding to therespective cells in the image are calculated and it is determinedwhether the value of the pixel of each coordinates is light (“1”) ordark (“0”) to obtain a 9-bit value per block. A method of converting aphotographed image into a binary image will be described later.

FIG. 5(B) illustrates a data type in which the center of 3×3 cells of ablock is fixed to be “1” (light) and its surrounding eight cells j1 toj8 are designed to include four light (“1”) cells and four dark (“0”)cells. In this case, one block has an information capacity of ₈C₄=70patterns, which is about 6 bits (6-bit expression).

FIG. 5(C) illustrates a data type in which the center of 3×3 cells of ablock is fixed to be “0” (dark) and its surrounding eight cells j1 to j8are designed to include four light (“1”) cells and four dark (“0”)cells. In this case as well, one block has an information capacity of₈C₄=70 patterns, which is about 6 bits (6-bit expression).

When the data type is 6-bit expression, both (B) and (C) can be used;however, the same data type is used on the encoding and decoding sides.

When analyzing the data type of FIG. 5(B) or (C), for a gray-scale imagegenerated from an input photographed image, the coordinate of the cellsj1 to j8 in the photographed image are calculated to obtain gray-scalepixel values of the respective cells, which are then sorted in thedescending order. In this case, the four light cells have high pixelvalues and the four dark cells have low pixel values. A method ofconverting a photographed image into a gray-scale image will bedescribed later.

It is demanded that a two-dimensional code be recognized under a varietyof photographing environments. Light has adverse effects on photographedimages, such as localized color changes and gradual color changes, andthese effects are the factors that make it difficult to generate anappropriate binarized image from a photographed image.

This method is advantageous in that it does not require a binarythreshold. The method has an effect of enabling to determine whethercells are light or dark based on the relationships of the relative pixelvalues of the cells, even without deriving a binary threshold. Inaddition, also against localized strong color changes caused by aspotlight or the like, since relevant cells are clustered into blocksand this increases the probability of all of the cells to be uniformlyaffected, even if the cells are entirely whitened, the relationships oftheir relative pixel values are maintained, so that the code is highlylike to be recognized.

In FIGS. 5(B) and (C), the central cell can be arbitrarily set to have avalue of “1” (light) or “0” (dark), and a data type in which thesurrounding eight cells j1 to j8 are designed to include four light(“1”) cells and four dark (“0”) cells is also possible. In this case,one block has an information capacity of ₈C₄×2=140 patterns, which isabout 7 bits (7-bit expression).

In the analysis method of this data type, the analysis of thesurrounding cells is carried out in the same manner as in the case of6-bit expression. In addition, in the analysis of the center pixel, thepixel value of the cell having the lowest pixel value among the fourpoints with high pixel values and the pixel value of the cell having thehighest pixel value among the four points with low pixel values aredefined as G1 and G2, respectively, and the coordinates of the cell inthe center of the block in the photographed image is calculated. Whenthe thus obtained pixel value is not smaller than (G1+G2)/2, the centralcell is determined to be a light cell. Otherwise, the central cell isdetermined to be a dark cell.

In this method, since the evaluation of the central cell utilizes athreshold value obtained from the analysis of the adjacent cells and itis highly likely that the central cell and its adjacent cells aresubjected to substantially the same effects of the photographingenvironment, the code can be recognized with high accuracy.

In FIGS. 5(D1) to (D8), in each block, the central cell is fixed to belight or dark (it is fixed to be light (“1”) in these figures) and itssurrounding eight cells are composed of four cells each of light anddark, with each of the eight cells being fixed to be light, dark, dark,light, light, light, dark and dark in the clockwise order, and the dataextraction starts at the position of an isolated light cell. In thiscase, since 8 patterns can be extracted, the data capacity is 3 bits(3-bit expression). In order to detect the position of the isolatedlight cell in this pattern, an arithmetic processing in which, from thecell at the starting position, the brightness value of each cell isadded, subtracted, subtracted, added, added, added, subtracted andsubtracted in the clockwise direction, is performed while sequentiallyrotating the starting position, and the starting position which yieldsthe maximum arithmetic result is thereby determined. The thus determinedstarting position is the position of the isolated light cell. Thisarithmetic processing can also be performed in the same manner with thelight and dark cells being reversed and, in this case, the startingposition which yields the minimum arithmetic result is determined.

As described above, in the first embodiment, according to thedata-block-type data (2 bits) in the format information blocks 17, anyone of the above-described 9-bit expression, 7-bit expression and 6-bitexpression is selected. If necessary, 3-bit expression may also beincluded in the selectable expressions.

In the first embodiment, the version information blocks and formatinformation blocks, which record important information, utilize a20-pattern-expression data type, which will now be described.

FIG. 6 illustrates 20-pattern-expression data type. In FIG. 6, areference number 31 represents a 20-pattern-expression data block, and areference number 32 represents any one of the first to fourth positiondetection patterns. As illustrated in FIGS. 6(A) and (B), in the datablock 31 arranged below or above the position detection pattern 32, thecells of the center column in the vertical direction are fixed to bedark-light-dark (0, 1, 0), and the data are expressed by 6 bits of thecells m1 to m6 in the two columns on each side. Further, by assigning 3bits of the 6 bits to be light and other 3 bits to be dark, ₆C₃=20patterns are expressed. The cell data of the blocks illustrated in FIGS.6(A) and (B) are detected by scanning the blocks in the verticaldirection. Further, as illustrated in FIGS. 6(C) and (D), in the datablock 31 arranged to the right or left of the position detection pattern32, the cells of the center column in the lateral direction are fixed tobe dark-light-dark (0, 1, 0), and the data are expressed by 6 bits ofthe cells m1 to m6 that are in the two columns above and below thecenter column. By assigning 3 bits of the 6 bits to be light and other 3bits to be dark, ₆C₃=20 patterns are expressed. The cell data of theblocks illustrated in FIGS. 6(C) and (D) are detected by scanning theblocks in the lateral direction.

By using this data type, even in a condition where the code version andthe cell size are unclear in the analysis, as long as the position of aposition detection pattern in a photographed image is determined, datacan be extracted from the data blocks. When the version and the cellsize are unclear, even if the coordinates of a position detectionpattern in a photographed image is known, the data block coordinatecannot be calculated. However, data blocks can be found by scanning inthe direction from a position detection pattern toward its adjacentposition detection pattern (the first and second position detectionpatterns are adjacent to the third and fourth detection patterns). InFIG. 6(A), scanning is performed toward the center of the data block inthe direction perpendicular to the lower side of the position detectionpattern represented by the reference number 32. The scanning startsimmediately below the position detection pattern, first hitting the darkcell on the upper side of the center column. Continuing the scanning,the scanning line hits the light cell, then the dark cell, and finallythe light cells of the separation space. By this, the coordinate of thecells in the center column and the number of pixels per cell of the datablock can be calculated. Consequently, the coordinates of other cells inthe data block are also easily determined, so that the data representedby the data block can be obtained.

The version information blocks and format information blocks are datablocks that are important in the analysis process. A 20-patternexpression is carried out by arranging these data blocks to have suchpositional relationships with respect to each position detection patternas illustrated in FIG. 6. As a measure against contamination andlocalized noises caused by a spotlight or the like, the same informationis maintained in the information blocks at two spots and in the formatinformation blocks at three spots.

FIG. 7 illustrates an example of a two-dimensional code generated inaccordance with the two-dimensional code of the first embodiment. Thetwo-dimensional code of FIG. 7 is a 11×11 block two-dimensional codehaving 43×43 cells, and its version is 3×3. The two-dimensional code ofFIG. 7 does not have any design region, and no design is embeddedtherein. Therefore, no design-embedding information block is necessary.

FIG. 8 illustrates another example of a two-dimensional code generatedin accordance with the two-dimensional code of the first embodiment. Thetwo-dimensional code of FIG. 8 is a 15×15 block two-dimensional codehaving 59×59 cells, and its version is 5×5. The two-dimensional code ofFIG. 8 contains a rectangular design region having diagonal corners atblock coordinates of (2, 5) and (11, 8), in which design region an imagedescribing an ID code and a product name is placed. By this, users candiscriminate the outline of the subject to be recognized even before thecode is recognized.

The position detection patterns, those having various shapes can beused, and the two-dimensional code can also take a variety of sizes andthe like.

FIG. 9 illustrates a two-dimensional code according to the secondembodiment. The two-dimensional code of the second embodiment isdifferent from that of the first embodiment in terms of the followingpoints.

(1) A first position detection pattern 52A has only a square framecomposed of dark cells with no square being arranged therein. Inaddition, second and third position detection patterns 52B and 52C bothhave a rectangular shape that is nearly a square. A fourth positiondetection pattern 52D has the same shape as that of the positiondetection pattern 12D of the first embodiment.

(2) The block size and the block constitution are different. Inparticular, the block constitution of the outer parts sandwiched betweenthe position detection patterns in both the lateral and verticaldirections is different. In these parts, a series of blocks, which aretwo vertical information blocks 55, two lateral version informationblocks 56, three format information blocks 57, two verticaldesign-embedding information blocks 58, two lateral design-embeddinginformation blocks 59, and position correction patterns 54A and 54B, isarranged.

The remaining blocks 60 are composed of actual data blocks, errorcorrection code blocks, blocks having position correction patterns, anddesign-embedding region(s).

Other parts are the same as those of the first embodiment; therefore,description thereof is omitted.

FIG. 10 illustrates an example of a two-dimensional code generated inaccordance with the two-dimensional code of the second embodiment.

FIG. 10(A) illustrates a 8×8 block two-dimensional code having 36×36cells. The two-dimensional code of FIG. 10(A) contains a rectangulardesign region having diagonal corners at block coordinates of (2, 2) and(5, 5), in which design region a high-resolution multi-valued image isplaced. This enables the two-dimensional code to have an improvedimpression and to draw attention.

FIG. 10(B) illustrates a 8×8 block two-dimensional code having 36×36cells. The two-dimensional code of FIG. 10(B) contains a rectangulardesign region having diagonal corners at block coordinates of (2, 3) and(5, 4), in which design region an image of numbers is placed.

There are various sizes and forms of two-dimensional codes and any ofthem can be applied to the two-dimensional code of the presentinvention.

FIG. 11 illustrates modification examples in which the positiondetection patterns of the two-dimensional code of the second embodimentare applied as two-dimensional patterns of different sizes and shapes. Areference number 53 represents the data region.

FIG. 11(A) illustrates an example of a square-form small two-dimensionalcode.

FIG. 11(B) illustrates an example of a two-dimensional code similar tothe two-dimensional code of the second embodiment.

FIG. 11(C) illustrates an example of a rectangular two-dimensional code.

FIG. 11(D) illustrates an example of a rectangular two-dimensional codein which a fifth position detection pattern 52E is added in the center.The fifth position detection pattern 52E is in a form similar to that ofthe first detection pattern 12A of the first embodiment which has asquare frame and a square therein.

Preferred forms of the position detection patterns will now be examined.

In the present invention, the following points are desired for theposition detection patterns: (1) the four types of position detectionpatterns can be distinguished from one another based on the shape, sizeor orientation on the two-dimensional code; (2) the types of theposition detection patterns can be distinguished from one another usinga simple algorithm; (3) for the thus distinguished position detectionpatterns, a combination thereof is easily determined (which contributesto high-speed recognition); (4) the position detection patterns have areduced cell size; (5) the position detection patterns can be easilydistinguished from a projected image other than the image of thetwo-dimensional code; and (6) no other position detection patternappears within the two-dimensional code.

It can be said that the position detection patterns of FIG. 2 and FIG. 9satisfy these matters.

Square and rectangular position detection patterns having variouscombinations of frame width and identification space width, i.e., cellsize, were generated. The thus generated position detection patternswere photographed such that the resulting images were blur and fuzzy,and the images were binarized to test whether or not the positiondetection patterns could be distinguished. Consequently, it wasdiscovered that the position detection patterns could be easilydistinguished from other projected images, depending on the presence orabsence of an identification space inside the frame; that a single-cellspace and a single-cell square therein are easily affected byblurriness; and that the width of the outer frame does not largelyaffect the tolerance to blurriness.

From these results, it was discovered that a square or rectangular framehaving a two-cell identification space inside is useful. The reason forthis is believed as follows. In a two-dimensional code in which thesmallest cell represents 1 bit, when blurriness or fuzziness occurs overan area of one cell or larger, even if the positions of the patternscould be detected, data cannot be acquired. Under normal photographingconditions, blurriness or fuzziness rarely occurs over an area of onecell or larger; therefore, an identification space of two cells in sizecan handle single-cell blurriness and fuzziness in all directions.

The second position detection pattern described in the first embodiment,which is a square of 4×4 in cell size, has a constitution of the minimumcell size that has the above-described space.

The first position detection pattern has a constitution in which asingle-cell-width frame, a two-cell space and a two-cell square arelayered. When the center of this position detection pattern is scanned,regardless of its orientation, a dark-light-dark-light-dark pattern isobtained, which is clearly different from the second position detectionpattern and noises.

As for the forms of the third and fourth position detection patterns, itis desired that the frames of the position detection patterns exist onthe extension of the frames of other position detection patterns. Bythis, when a position detection pattern is missing, the accuracy ofestimating the coordinates of the missing position detection pattern canbe improved.

The forms of the third and fourth position detection patterns of thefirst embodiment comply with these conditions. Since these positiondetection patterns are each tilted by 90° and have an aspect ratio thatis different from those of the first and second position detectionpatterns, the third and fourth position detection patterns can be easilydistinguished from the first and second position detection patterns.

The second embodiment has a constitution in which the cell size occupiedby the position detection patterns is the smallest. The first and secondposition detection patterns have the same shape but different sizes,with the second position detection pattern having a size of 5×5 cells.For the same reason as described above, the third and fourth positiondetection patterns are generated.

These position detection patterns have a cell size of 16+64+32+32=144cells in the first embodiment and 16+25+20+20=81 cells in the secondembodiment.

Despite the two-dimensional code illustrated in FIG. 1 has positiondetection patterns only at three spots, these three position detectionpatterns have a cell size of 7×7×3=147 cells, which is larger than thoseof the embodiments of the present invention.

The first embodiment has a larger cell size than the second embodiment;however, the position detection patterns of the second embodiment allhave similar areas in size and their detection accuracy is thus likelyto be affected when they are photographed at an angle. Meanwhile, in thefirst embodiment, the first and second position detection patterns havedifferent forms and the third and fourth position detection patterns arein different orientations. The first and second position detectionpatterns are different from the third and fourth position detectionpatterns in terms of the aspect ratio. These position detection patternscan be adequately distinguished even when they are photographed at anangle, which is a constitution useful for distinguishing the positiondetection patterns.

Further, around each of the position detection patterns of FIG. 2, lightcells are arranged as a 2-cell blank space. Recognition of thetwo-dimensional code of FIG. 1 requires a quiet zone around the printedcode, and this quiet zone is regarded as a part of the code. Incontrast, the accuracy of recognizing the two-dimensional code of thefirst embodiment is not affected regardless of the type of a printplaced around the code. Moreover, as in the second embodiment of FIG. 9,a blank space can also be arranged outside the code in the same manneras for the code of FIG. 1.

In the spirit of the present invention, position detection patterns ofother forms can also be used and various modifications can be made.

FIG. 12 illustrates four position detection patterns of eachmodification example.

FIG. 12(A) illustrates an example where one large circular frame, twoelliptical frames with different orientations and one small circularframe constitute four position detection patterns.

FIG. 12(B) illustrates an example where one large circular frame havinga small circle inside, two elliptical frames with different orientationsand one small circular frame constitute four position detectionpatterns.

FIG. 12(C) illustrates an example where one large cross, two crosses,which are extended in only one direction but have different directionsof the extension, and one small cross constitute four position detectionpatterns.

FIG. 12(D) illustrates an example where one large L-shaped pattern, twoL-shaped patterns, which are extended in only one direction but havedifferent directions of the extension, and one small L-shaped patternconstitute four position detection patterns. These L-shaped patterns areall in the same orientation and their rotational direction can bedetermined from the corner position. These L-shaped patterns may also berotated by 90°.

FIG. 12(E) illustrates an example where one large triangular frame, twotriangular frames, which are extended in only one direction but havedifferent directions of the extension, and one small triangular frameconstitute four position detection patterns.

FIG. 12 illustrates only some of the possible examples, and positiondetection patterns of other various forms can be used as well.

Next, the process of generating the two-dimensional codes of the firstand second embodiments (encoding process) will be described.

FIG. 13 illustrates an example of a client-server configuration, whichis a hardware configuration of a system for generating and providing atwo-dimensional code upon a request.

The generating system comprises: a user hardware which is operated by auser who determines the specifications and requests a two-dimensionalcode to be generated; and a system hardware which generates and providesthe requested two-dimensional code.

The user hardware comprises: a user processing unit 61, such as acomputer; and a memory device 62, such as a magnetic disk.

The system hardware comprises: a system processing unit 65, such as acomputer; and a memory device 66, such as a magnetic disk.

The user processing unit 61 and the system processing unit 65 areconfigured to enable communication therebetween, being connected througha communication line or the like.

Printing is performed on the user side; however, it may also beperformed on the system side or at other printing place. Atwo-dimensional code may be printed on any medium such as a sheet ofpaper, a resin plate or a casing surface. A design to be embedded may beprinted on the medium in advance, and a two-dimensional code is printedafter setting the medium such that the printed design to be embedded isfitted into the design region.

Any printing apparatus can be employed as long as it is capable ofprinting a two-dimensional code on the above-mentioned media, and theprinting apparatus may be, for example, a simple printer, a precisionprinters, or other printing apparatus capable of performing not onlymonochrome printing but also color printing. The generatedtwo-dimensional code may also be transmitted as two-dimensional codedata to the user via the communication line, without being printed. Theuser, as required, then transmits the data to a third party display orthe like so that the generated two-dimensional code is displayed.

FIG. 13 illustrates an example of generating system having aclient-server configuration; however, the generating system is notrestricted thereto. A variety of modifications can be made and thegenerating system may take, for example, a configuration in which atwo-dimensional code is issued by encoding software on a client's PC andthen printed by a USB-connected printer, or a configuration in which atwo-dimensional code is issued from a hand-held terminal printer.

FIGS. 14 to 16 are flow charts illustrating the procedures of theencoding process in which a user accesses the system hardware via theuser hardware and generates a desired two-dimensional code.

In the step S10, the user initiates the main encoding process.

In the step S11, the user inputs a message(s) to be recorded in atwo-dimensional code.

In the step S12, the user decides whether or not to embed a design intothe two-dimensional code. If the user decided to embed a design, theuser proceeds to the step S13 and, if the user decided not to embed adesign, the user proceeds to the step S15, which is carried out in thesystem side. In the latter case, the user processing unit 61 notifiesthe system processing unit 65 about the message(s) and the absence ofdesign to be embedded.

In the step S13, the user inputs the position of the block into whichthe design is embedded (design-embedding offset width, design-embeddingoffset height, design-embedding width and design-embedding height). Theuser processing unit 61 notifies the system processing unit 65 about theinput message(s), the presence of a design to be embedded and theposition of the block(s) into which the design is embedded.

In the step S14, in the system side, the block size of the design isdetermined based on the transmitted block position.

In the step S15, the block size for recoding the transmitted message(s)is determined.

In the step S16, the minimum vertical version is calculated for alllateral versions. In this calculation, from a value obtained bymultiplying the number of vertical blocks by that of lateral blocks, thenumber of the position detection pattern blocks, the version informationblocks and the format information blocks as well as, when a design isembedded, the design-embedding information blocks, the blockscorresponding to the design-embedding region and the position correctionpattern blocks, is subtracted to determine the number of remainingblocks. Further, from this number of blocks, the number of errorcorrection code blocks arranged to attain a certain error correctionrate is subtracted, and the size of the message-recording actual datablocks that can be contained is indicated in a table form. The systemprocessing unit 65 transmits the thus calculated table data to the userprocessing unit 61.

In the step S17, a table of the vertical-lateral versions is indicatedto the user, and the user determines which version to be used. The userprocessing unit 61 transmits the thus determined vertical-lateralversion to the system processing unit 65.

In the step S18, in the system side, based on the transmittedvertical-lateral version and the block size corresponding to thedesign-embedding region, the block size of the actual data isdetermined.

In the step S19, in the system side, based on the transmittedvertical-lateral version and the block size corresponding to thedesign-embedding region, the block size of the error-correcting code isdetermined.

In the step S20, in the system side, the positions of the versioninformation blocks and format information blocks are determined. Inaddition, when a design is embedded, the positions of thedesign-embedding information blocks and design-embedding region blocksare also determined.

In the step S21, in the system side, it is determined whether or not adesign is embedded. When a design is embedded, the system proceeds tothe step S22, while when no design is embedded, the system proceeds tothe step S23.

In the step S22, the design-embedding information blocks are arranged atprescribed positions on the code image part.

In the step S23, the position detection patterns and the positioncorrection patterns are arranged on the image part.

In the step S24, the version information blocks and the formatinformation blocks are arranged on the image part.

In the step S25, a message header is added to each message.

In the step S26, it is determined if there is still a space left forputting data. When there is a space left, the system proceeds to thestep S27, while when there is no space left, the system proceeds to thestep S29.

In the step S27, an end message header (end flag) is added to the end ofthe message data.

In the step S28, padding is added to the remaining actual data region.

In the step S29, the actual data are made into blocks and arranged onthe image part.

In the step S30, the error correction code blocks are arranged on theimage part.

In the step 31, the system processing unit 65 outputs and transmits acode image generated in the above-described manner to the userprocessing unit 61.

In the step 32, in the user side, it is determined whether or not adesign is embedded. When a design is embedded, the user proceeds to thestep S33, while when no design is embedded, the user proceeds to thestep S34 to finish the encoding process.

In the step S33, a whole image is generated by integrating thetransmitted code image with the data of the design to be embedded intothe block(s) of the design-embedding region. The embedding of the designmay also be performed by the system processing unit in the form of, forexample, data attachment.

In the step S34, the main encoding process is finished.

In the above-described embodiment, the user side has the design data;however, the design data may be stored in the system side and specifiedby the user.

FIG. 17 illustrates a hardware configuration of a two-dimensional codeanalyzer which reads out and analyzes the two-dimensional code of thefirst embodiment.

The two-dimensional code analyzer comprises: a reading unit 70; acomputer (two-dimensional code analysis/processing unit) 74; a display75; and a communication interface 76. The reading unit 70 comprises: alens 71; an image sensor 72; and an analog-digital converter (AD) 73,and outputs digital image data of photographed two-dimensional code tothe computer 74. The two-dimensional code analyzer illustrated in FIG.17 is widely used and, in recent years, portable terminals have alsorealized the same functions as those of the two-dimensional codeanalyzer.

FIGS. 18 to 20 are flow charts illustrating the procedures of thedecoding process in which two-dimensional codes photographed by the userare analyzed. This decoding process assumes a case where pluraltwo-dimensional codes are projected on a single screen. The decodingprocess consists of a main analysis process and an informationextraction process. First, the main analysis process will be described.

In the step S101, the main analysis process is initiated.

In the step S102, photographed images of two-dimensional codes areinput.

In the step S103, binary images of each input photographed image aregenerated. As for the binarization method, when the input photographedimage is a color image such as an RGB image, it is once converted into agray-scale image. An average of the maximum and minimum brightnessvalues in the image is taken as a threshold value, and pixels with avalue of not less than the threshold value are defined to be “light” andpixels with a value of less than the threshold value are defined to be“dark”. The gray-scale conversion of the color image is carried outusing the RGB values of the respective pixels, in accordance with aconversion formula: Brightness=0.299R+0.587G+0.114B. The conversionmethod is not restricted to the above-described one as there have beenproposed a variety of methods for conversion of a color image into agray-scale image as well as for further conversion of the gray-scaleimage into a binary image.

In the step S104, candidate position detection patterns are detected.Specifically, starting at an upper left point of the image, the image isscanned in the X direction and, once reaching the right edge, the imageis scanned in the X direction from the left edge starting at severalpixels below. In other words, several pixels are omitted from thescanning. This scanning operation is repeated for the entire image. Thenumber of the omitted pixels is: (Maximum number of omittedpixels)=(Minimum cell height of position detection pattern)×(Number ofpixels per cell in photographing). Taking into consideration therotation of the code as well, the minimum height of a position detectionpattern refers to the minimum cell size in the Y direction that can beobtained by rotation of the position detection pattern and, in thepresent embodiment, the upper-left second position detection pattern inan unrotated state has a minimum height of 4 cells. When the number ofpixels per cell in photographing is less than 1, even in an ideal image,it is difficult to distinguish a light cell from a dark cell.Considering displacement and rotation of cells in actual photographedimages, it is desired that each cell have at least 3 pixels. When eachcell has 3 pixels, the maximum number of the omitted pixels in theabove-described case is 12 and the number of the image scanningoperations is thus 1/12 of the total number of the pixels, so that thenumber of the scanning operations can be largely reduced.

In the step S105, the candidate position detection patterns areexamined. Specifically, when a boundary between light and dark parts isfound, the periphery of the dark part is scanned. In this process, theminimum and maximum X and Y coordinates of the dark part are determined.As a result, the circumscribing rectangle of the dark lump can beobtained. The upper left coordinates of this rectangle is represented as“(x1, y1)” and the lower right coordinates is represented as “(x2, y2)”.Once the periphery is scanned, no more scanning thereof is necessary.

Even if such periphery exploration is performed, the number of the imagescanning operations can be sufficiently reduced. One example of worstcase where the processing time becomes the longest due to such peripheryexploration is when one-pixel vertical stripes are arranged at one-pixelintervals. However, such a case does not occur in the first place and,even if it did, the number of the perimeter exploration operations canbe maintained to be the same as the number of the scanning operationsrequired for scanning all pixels once; therefore, the number of thescanning operations is not increased. The same also applies to otherworst case scenarios.

In the case of the two-dimensional code of FIG. 1, the positiondetection patterns can be detected by exploring parts having adark-light-dark-light-dark ratio of 1:1:3:1:1, which means that theposition detection patterns can be found by one-time scanning. When thephotographed code is tilted at an angle of 45°, the ratio of 1:1:3:1:1can be obtained only when the code is scanned diagonally. Thephotographing orientation is freely selected in many cases; therefore,the orientation of the photographed code can be in any rotationalposition of 360°. In such cases, the number of the omittable scanningoperations is small, and it cannot be increased because the actualrotational position is not known.

FIG. 21 illustrates checking of the shapes of the candidate positiondetection patterns.

Next, the forms of the candidate position detection patterns arechecked. The position detection patterns of the two-dimensional code ofthe first embodiment all have a frame shape, i.e., a hollowed shape.Thus, the presence or absence of a hole is verified. With the startingpoint being set at the central point on the left side of thecircumscribing rectangle (x1, (y1+y2)/2) and the end point being set at(x2, (y1+y2)/2), scanning is performed in the x-axis direction. In thisprocess, it is confirmed that the following condition (1) or (2) issatisfied.

(1) The presence of a dark-light-dark sequence is confirmed. It is alsoconfirmed that the pixel in the center between the leftmost first darkpixel (l×1) and the rightmost second dark pixel (r×1) is light.

(2) A dark-light-dark-light-dark pattern is searched. It is conformedthat the pixel in the center between the leftmost first dark pixel (l×2)and the rightmost second dark pixel (r×2) is dark.

Further, in the case of (1), as illustrated in FIG. 21(A), scanning isalso performed in the vertical direction from the center coordinates((l×1+r×1)/2, (y1+y2)/2). The scanning of the upper part yields alight-dark-light sequence (end point: ((l×1+r×1)/2), y1−1)), and thescanning of the lower part also yields a light-dark-light sequence (endpoint: ((l×1+r×1)/2), y2+1)). It is confirmed that the middle pointbetween the y-coordinates (ty1), which is at the boundary of dark andlight on the upper side, and the y-coordinates (by1), which is at theboundary of dark and light on the lower side, has substantially the samecoordinates as that of the light pixel in the center.

In the case of (2) as well, as illustrated in FIG. 21(B), scanning isalso performed in the vertical direction from the center coordinates((l×2+r×2)/2, (y1+y2)/2). The scanning of the upper part yields adark-light-dark-light sequence (end point: ((l×2+r×2)/2), y1−1)), andthe scanning of the lower part also yields a dark-light-dark-lightsequence (end point: ((l×2+r×2)/2), y2+1)). It is confirmed that themiddle point between the y-coordinates (ty2), which is at the boundaryof the second dark part and the second light part on the upper side, andthe y-coordinates (by2), which is at the boundary of the second darkpart and the second light part on the lower side, has substantially thesame coordinates as that of the light pixel in the center.

By the above-described processing, the first position detection patternhaving a dark part in a frame (a square in a square frame) can bedistinguished from the second to fourth position detection patternshaving only a frame (a square or rectangular frame: box-form).

A pattern that does not satisfy the condition of (1) or (2) is not aposition detection pattern.

Next, the apexes of each position detection pattern are explored. Eachposition detection pattern is scanned in the x-axis direction from theupper-left coordinates (x1, y1) of the circumscribing rectangle to thecoordinates (x2, y1). The coordinates of the first dark point cominginto contact is designated as “vortex 1” (vx1, vy1). The positiondetection pattern is then scanned in the y-axis direction from theupper-right coordinates (x2, y1) to the coordinates (x2, y2). Thecoordinates of the first dark point coming into contact in this scanningis designated as “vertex 2” (vx2, vy2). The position detection patternis further scanned in the opposite x-axis direction from the lower-rightcoordinates (x2, y2) to the coordinates (x1, y2). The coordinates of thefirst dark point coming into contact in this scanning is designated as“vertex 3” (vx3, vy3). Thereafter, the position detection pattern isscanned in the opposite y-axis direction from the lower-left coordinates(x1, y2) to the coordinates (x1, y1). The coordinates of the first darkpoint coming into contact in this scanning is designated as “vertex 4”(vx4, vy4). The vortexes 1 to 4 should form a rectangle (including asquare). If not, the scanned pattern is not a position detectionpattern. Description of FIG. 21(B) is omitted.

Subsequently, the aspect ratio of the rectangle is examined. The lengthof one side of the rectangle is determined as((vx1−vx2)×(vx1−vx2)+(vy1−vy2)×(vy1−vy2))^(1/2), and the length of theother side is determined as((vx2−vx3)×(vx2−vx3)+(vy2−vy3)×(vy2−vy3))^(1/2). When the rectangle hasan aspect ratio, (long side):(short side), of 1:1 and the form of (1),it is the second position detection pattern; when the rectangle has anaspect ratio, (long side):(short side), of 1:1 and the form of (2), itis the first position detection pattern; and when the rectangle has anaspect ratio, (long side):(short side), of 1:2 and the form of (1), itis the third or fourth position detection pattern. So far, these threetypes of position detection patterns can be distinguished from eachother.

Next, the area of each position detection pattern is determined. It isnoted here that this “area” refers to the area of the outer rectangularframe and thus includes the area of the inside space. In the case of thefirst position detection pattern, the area of the square inside theframe is also included. The area of each position detection pattern canbe determined by subtracting the areas of the four right-angledtriangles including the four corners from the area of the outerrectangle:Area=(x2−x1)×(y2−y1)−(vx1−vx4)×(vy4−vy1)/2−(vx2−vx1)×(vy2−vy1)/2−(vx2−vx3)×(vy3−vy2)/2−(vx3−vx4)×(vy3−vy4)/2.

Then, the rotation angle is determined. For the first and secondposition detection patterns, since they are squares and a tilt of 90° orlarger thus cannot be detected, a tilt angle is determined up to 90°.The angle is expressed in terms of clockwise rotation.

θ=arctan((vy2−vy1)/(vx2−vx1))

(wherein, θ represents a rotation angle)

For the third and fourth position detection patterns, the rotation angleis determined in a range of 0° to 180°. For the third position detectionpattern, the distance between two coordinate is defined by a function:Length (x1, y1, x2, y2)=((x2−x1)²+(y2−y1)²)^(1/2). In a range of 0° to45°, length (vx1, vy1, vx2, vy2)>length (vx4, vy4, vx1, vy1) and(x2−x1)>(y2−y1), and the rotation angle is determined by:θ=arctan((vy2−vy1)/(vx2−vx1)). In a range of 45° to 90°, length (vx1,vy1, vx2, vy2)>length (vx4, vy4, vx1, vy1) and (x2−x1)<(y2−y1), and therotation angle is determined by: θ=arctan((vy2−vy1)/(vx2−vx1)). In arange of 90° to 135°, length (vx1, vy1, vx2, vy2)<length (vx4, vy4, vx1,vy1) and (x2−x1)<(y2−y1), and the rotation angle is determined by:θ=arctan((vy2−vy1)/(vx2−vx1))+90°. In a range of 135° to 150°, length(vx1, vy1, vx2, vy2)<length (vx4, vy4, vx1, vy1) and (x2−x1)>(y2−y1),and the rotation angle is determined by:θ=arctan((vy2−vy1)/(vx2−vx1))+90°. The rotation angle θ of the fourthposition detection pattern is also determined in the same manner.

Next, the center coordinates of the position detection patterns aredetected. The center coordinates is defined as the center of thecircumscribing rectangle, which is ((x1+x2)/2(y1+y2)/2).

As a result of the above-described operations, the examination of thecandidate position detection patterns is completed.

In the step S106, the position detection patterns that have already beendifferentiated into three types are sorted in the descending order ofarea for each type.

In the step S107, a combination of the four types of position detectionpatterns is generated. First, among the candidates for the firstposition detection patterns, one which has the largest area is selected.With the area of this first position detection pattern being defined asS, a candidate for the second position detection pattern which as acombination of an area of S/4 and the same rotation angle is searched.Once the second position detection pattern is found, candidates for thethird and fourth position detection patterns that have an area of S/2are searched. Further, a combination of a candidate having the samerotation angle and a candidate having a rotation angle different by 90°is searched.

When a plurality of two-dimensional codes are projected on a singlescreen, considering all kinds of combinations of the candidate positiondetection patterns, there is an enormous number of possible positiondetection pattern combinations. As in the present invention, by usingposition detection patterns that are all different from each other, thenumber of possible combinations can be largely reduced. In addition, byapplying the characteristics determined in advance, such as shape, areaand rotation, the combinations can be further narrowed down with simplecomparative mathematical operation. This operation will be describedlater.

In the step S107, it is determined whether there is or is not anycombination of the four position detection patterns left unexamined. Ifthere is, the operation proceeds to the step S108 and, if not, theoperation proceeds to the step S112.

In the step S108, information is extracted from combined positiondetection patterns that are considered to belong to the sametwo-dimensional code. This process will be described later referring toFIGS. 19 and 20.

In the step S109, depending on the result of the information extraction,when the extraction was successful, the operation proceeds to the stepS110, while when the extraction failed, the combination of positiondetection patterns for which the extraction failed is excluded, and theoperation returns back to the step S107.

In the step S110, the message of the successfully extracted informationis saved.

In the step S111, the candidates used for the two-dimensional patternfrom which data were successfully extracted are excluded from thecandidate position detection patterns, and the operation returns back tothe step S107. When an unused candidate position detection pattern isincluded in the range of the two-dimensional pattern from which datawere successfully extracted, it is also excluded from the candidates.

By repeating the steps S107 to S111, the analysis of projectedtwo-dimensional codes is completed. When there are still candidateposition detection patterns that have not been excluded, forcombinations of two or more thereof, the information extraction of thestep S108 may be carried out. This will be described later.

In the step S112, an analysis completion message is transmitted to thecalling source.

In the step S113, the main analysis process is finished.

Next, the information extraction process of the step S108 will bedescribed referring to FIGS. 19 and 20. In the step S200, informationextraction is initiated.

In the step S201, the relationship of four position combination patternsin a given combination is checked. This checking is done by determiningwhether the below-described conditions (a) and (b) are satisfied. Whenany of these items is not satisfied, the presence of a problem isassumed and the information extraction process is terminated.

First, the center coordinate of the first, second, third and fourthposition detection patterns are defined as pt1, pt2, pt3 and pt4,respectively, and these points are then connected in the order of pt1,pt3, pt2, pt4 and pt1. A rectangle is thereby obtained when thecombination of the four position detection patterns is correct.

(a) All of the corners have a right angle.

(b) The opposing sides have the same length (1:1).

In the step S202, the presence or absence of a problem is determinedbased on the result of the above-described checking. When there was aproblem, the operation proceeds to the step S203 where a flag indicatingfailed information extraction is placed, while when there was noproblem, the operation proceeds to the step S204.

In the step S204, from any one of the position detection patterns, thenumber of pixels per cell is determined. In the case of the secondposition detection pattern, it has an area of 4×4=16 cells, and thenumber of pixels per cell is determined by an equation: Number of pixelsper cell=((area)/16)^(1/2).

In the step S205, the distance between the center coordinate of adjacentposition detection patterns is measured in each of the vertical andlateral directions and the thus obtained distance values are eachdivided by the value determined in the step S204, thereby the cell sizeof the two-dimensional code in the vertical and lateral directions canbe determined. With the thus obtained lateral distance between thecenter coordinate being defined as “d” pixels and the number of pixelsper cell being defined as “p” pixels/cell, the lateral cell size of thecode is determined by an equation: Code lateral cell size=d/p+(4+6). Thevertical cell size is also determined in the same manner.

In the step S205, based on the thus determined cell sizes, the versionof the two-dimensional code is tentatively decided. The version numberstepwisely increases every 8 cells. Since the lateral cell size of thecode is determined by an equation: Code lateral cell size=lateralversion×8+19, the lateral version of the code can be determined bymodifying this equation to: Lateral version=(cell size−19)/8. The thusobtained lateral version number is used as a tentative lateral version.When there is no version that matches the cell size, a version with theclosest cell size is designated. The tentative vertical version is alsodecided in the same manner. The reason why the thus decided versions aretentative is because there is the possibility that accurate values maynot be obtained due to photographing at an angle, bending of the printedpaper or the like is taken into consideration. The version informationblocks are also used in combination so that accurate values can beobtained.

In the step S206, by scanning the two-dimensional code in the directionsof each position detection pattern to its adjacent position detectionpatterns, the coordinates of the cells constituting the versioninformation blocks and format information blocks in the photographedimage are detected.

In the step S207, the (vertical and lateral) version information blocksare analyzed. As a result, the vertical and lateral versions aredetermined. Failure of the analysis leads to termination of theoperation. As described above, the version information blocks and theformat information blocks each indicate 20 values. As the vertical andlateral version information blocks, each type is arranged at two spots.When the values that are read out from the vertical and lateral versioninformation blocks each arranged at two spots are identical to at leasttwo of the three values of the tentative version information obtainedfrom the code width, the code height and the position detection patternsize, those values are adopted.

In the step S208, the format information blocks are analyzed. Thepresence or absence of a design to be embedded and the data embeddingmethod for each block are thereby determined. Failure of the analysisleads to termination of the operation. The format information blocks arearranged at three spots and, when two or more thereof yielded the sameresults, these results are adopted.

In the step S209, the coordinates of a position correction pattern iscalculated and the coordinate of each cell in the image of thetwo-dimensional code are determined with high precision. Although thecoordinate of the cells have already been derived, the positioncorrection pattern allows the effects of lens distortion to be reduced.Since the coordinates of the position correction pattern in the imagehave already been determined, it is confirmed that the point at thecoordinates is dark. Then, starting from this point, scanning isperformed toward the right-hand side to find the boundary of dark andlight pixels, and the periphery thereof is then scanned in the samemanner as in the step S105. With the upper-left and lower-rightcoordinate of the circumscribing rectangle being defined as (x1, y1) and(x2, y2), respectively, the center coordinates are obtained as((x1+x2)/2, (y1+y2)/2)).

In the step 210, the presence or absence of a design to be embedded inthe format information blocks is determined. When the presence wasdetermined, the operation proceeds to the step S211, and when theabsence was determined, the operation proceeds to the step S212.

In the step S211, by referring to the design-embedding informationblocks, the vertical and lateral offset width and height of thedesign-embedding block as well as the width and height of thedesign-embedding block are determined.

In the step S212, with respect to the actual data blocks and errorcorrection code blocks, any nearest four points are selected from thecenter coordinate of the position detection patterns and those of theposition correction patterns, and the coordinate of the cells in thephotographed image are determined by projective transformation.

In the step S213, with respect to the actual data blocks and errorcorrection code blocks, in accordance with the data type of the formatinformation blocks, a plurality of light (1) and dark (0) data aredetected.

In the step S214, from the number of the actual data blocks and errorcorrection code blocks, the number of the error correction codes iscalculated. By this, the actual data and the error correction codes aredetermined.

In the step S215, with respect to the data region and the errorcorrection codes, the number and positions of errors are detected usingthe error correction codes. When the number of errors is 0, theoperation proceeds to the step S219. Otherwise, the operation proceedsto the step S216.

In the step S216, it is determined whether or not the errors arecorrectable. When the errors are correctable, the operation proceeds tothe step S218, while when the errors are not correctable, the operationproceeds to the step S217.

In the step S217, since no message was obtained due to the failure ofinformation extraction, the operation is terminated.

In the step S218, using the error correction codes, the errors in theactual data are corrected.

In the step S219, the resulting actual data are composed of a header(s)(message type (message encode)-message size), a message(s), an end flagand padding. A combination of a header and a message is defined as asegment. An end flag is a special segment which does not contain anymessage. There may be a plurality of segments. When an end flag isfound, what follows the end flag is all padding. From the data, themessage(s) is/are reconstructed.

In the step S220, the information extraction process is finished.

Projective transformation requires at least 4 sets of coordinate. Forthe above-described analysis process, a case where four positiondetection patterns can be detected was described; however, due tocontamination, blurriness, fuzziness or the like of the image, it ispossible that only three or two position detection patterns can bedetected. In the present invention, in such a case, since the detectedthree or two position detection patterns have different shapes, thetype(s) of the undetected position detection pattern(s) is/aredetermined from the positional relationships of the detected three ortwo position detection patterns; therefore, the positions of theundetected position detection patterns can be easily estimated. Forexample, in the two-dimensional code of the first embodiment, when threeposition detection patterns are detected, since two position detectionpatterns that are arranged diagonally to each other can be identifiedbased on their shapes, it can be estimated that the undetected positiondetection pattern is arranged, with respect to the straight lineconnecting the two diagonally-arranged position detection patterns, at amirror-symmetrical position of the other position detection pattern.Further, when two position detection patterns are detected, thepositional relationship of the two position detection patterns isdetermined based on their shapes. For example, if these two positiondetection patterns are arranged adjacent to each other, it is estimatedthat the remaining two position detection patterns exist at positionsthat are away from the straight line connecting the two detectedposition detection patterns at the same distance in the directionperpendicular to the straight line. Meanwhile, if the two detectedposition detection patterns are arranged diagonally to each other, it isestimated that the remaining two position detection patterns exist atthe intersections of the lines extending from each side of the twodetected position detection patterns. For example, when the third andfourth position detection patterns are identified, extension of the twoshort sides of each of these position detection patterns yields a totalof four intersections, which correspond to the four apexes of the firstposition detection pattern. In the same manner, the four intersectionsformed by extending the long sides correspond to the apexes of thesecond position detection patterns. Also when the first and secondposition detection patterns are identified, the positions of theremaining two position detection patterns can be estimated by the samemethod. Needless to say, as compared to a case where all four positiondetection patterns are detected, the estimation accuracy is reduced whenthree of them are detected, and the estimation accuracy is furtherreduced when only two of them are detected. In any case, the positionsof the four position detection patterns are tentatively decided in theabove-described manner, and they are applied to projectivetransformation so as to obtain the positional information on theposition correction patterns. Then, the position correction patterns areutilized for coordinate corrections, and the coordinate of the fourposition detection patterns are ultimately determined, based on thecoordinate of the detected position detection patterns and theircoordinate thus corrected by the position correction patterns.

Considering that there may be an undetectable position detectionpattern(s) due to contamination or the like, a larger number of theposition detection patterns is more desirable; however, an increase inthe number of the position detection patterns not only increases thearea ratio represented by the position detection patterns and therebyreduces the data efficiency, but also increases the work load requiredfor detection of the position detection patterns. Therefore, it isdesired that the number of the position detection patterns be decided asappropriate in accordance with the mode of use and the like of thetwo-dimensional code.

Next, for a case where a plurality of two-dimensional codes areprojected on a single screen, the use of the two-dimensional code of thepresent invention is compared with the use of the two-dimensional codeof FIG. 1. For example, when six of the two-dimensional code of FIG. 1is projected on a single screen, 18 identical position detectionpatterns are projected on the screen. It is supposed that, as describedabove, the 18 position detection patterns are detected and, for allcombinations of three position detection patterns, it is checked if thethree position detection patterns of each combination belong to the sametwo-dimensional code. In this case, the number of the combinations is₁₈C₃=816. If one two-dimensional code contains four identical positiondetection patterns, the number of the position detection patternsprojected on the screen is 24, which means that the number of thecombinations is ₂₄C₄=10,624. In this manner, the number of suchcombinations is huge and this leads to an increase in the processingtime.

In contrast, when the position detection patterns are different as inthe case of the present invention, the number of combinations of threedifferent position detection patterns is ₆C₁×₆C₁×₆C₁=216 and that offour different position detection patterns is ₆C₁×₆C₁×₆C₁×₆C₁=1,296, sothat the number of such combinations is largely reduced.

Further, in the above-described analysis process, the position detectionpatterns are detected by scanning while some parts of the screen areomitted from the scanning; however, as long as one candidate positiondetection pattern can be found, from its shape, it is possible toestimate the orientation and distance range of other position detectionpatterns to a certain extent and, by restricting the scanning to theirregions, the efficiency of detecting the position detection patterns canbe improved. For example, in the two-dimensional codes of the first andsecond embodiments, it can be estimated that the second positiondetection pattern exists on the extension of the long sides of the thirdand fourth position detection patterns and that the first positiondetection pattern exists on the extension of the short sides, which areperpendicular to the respective long sides, of the third and fourthposition detection patterns. When two or three position detectionpatterns are detected, the regions in which other position detectionpattern(s) can be expected to exist are further limited.

In the above-described two-dimensional codes, four different positiondetection patterns are arranged; however, data can be extracted withhigh accuracy also from a two-dimensional code having a constitution inwhich three different position detection patterns and one or moreposition correction patterns are arranged. In this case, the positiondetection patterns are arranged in such a manner that one of the fourposition detection patterns is absent.

In the analysis of such a two-dimensional code, after detecting thethree position detection patterns, the coordinates of the part lacking aposition detection pattern are extrapolated from the positionalrelationships of other position detection patterns. However, when thetwo-dimensional code is photographed at an angle from above, it isconcerned that the extrapolated coordinates might contain an error.Therefore, from a total of four sets of coordinates, which are thecoordinates of the three position detection patterns and theextrapolated coordinates, the coordinates of the position correctionpattern that is closest to the part of the missing position detectionpattern are obtained by projective transformation.

Then, the position correction pattern is scanned to correct itscoordinates. Next, using a total of four sets of coordinates, which arethe coordinates of the three position detection patterns and oneposition correction pattern, mapping of the data coordinates is carriedout. The position correction pattern has an effect of reducing errors incoordinates and thereby enables acquisition of highly accuratecoordinates, so that data can be extracted with high accuracy even froma two-dimensional code having three position detection patterns and oneor more position correction patterns.

When a position correction pattern is already arranged, since the numberof the position detection patterns is reduced by one, the efficiency ofthe code is improved. On the other hand, the redundancy of the positiondetection patterns is reduced, and this leads to a reduction in thetolerance to contamination and the like.

Further, it is not always that only one photographed image is input, anda case where an image synthesized from a plurality of input images isanalyzed can also be considered. Examples of such a case include thosecases where an image is produced from time-series consecutive imagessuch as an animation and this image is analyzed, and those cases where acode image is divided into plural pieces and then input.

Moreover, such an application where a single data set is obtained bydisplaying different codes in series by animation and recognizing all ofthese codes can also be considered. In this case, a plurality of codesmay also be arranged on a paper, not in an animation format.

The two-dimensional code of the present invention can also be applied tothese cases.

Thus far, embodiments of the present invention have been described;however, these descriptions of the embodiments are provided simply forthe purpose of explaining the present invention, and it will beunderstood by those of ordinary skill in the art that variousmodifications can be made within the scope of claims.

DESCRIPTION OF SYMBOLS

-   -   12A First position detection pattern    -   12B Third position detection pattern    -   12C Fourth position detection pattern    -   12D Second position detection pattern    -   15 Version information block (vertical)    -   16 Version information block (lateral)    -   17 Format information block    -   18A-18B Design-embedding information block (vertical)    -   19A-19B Design-embedding information block (lateral)

1-9. (canceled)
 10. A two-dimensional code comprising cells representingbinary-coded data that are arranged as a pattern in the form of atwo-dimensional matrix, wherein the two-dimensional code comprises:position detection pattern; plural data blocks created by dividing aregion of the two-dimensional matrix that excludes the part of theposition detection pattern; and a separation space arranged between theplural data blocks that are adjacent, the plural data blocks beingdivided in accordance with the unit of error correction.
 11. Thetwo-dimensional code according to claim 10, wherein the plural datablocks comprise format information blocks indicating which of pluralexpressions is represented by the data blocks.
 12. The two-dimensionalcode according to claim 10, wherein the position detection pattern hasan area larger than the data block.
 13. The two-dimensional codeaccording to claim 10, wherein the separation space is entirely light orentirely dark.
 14. The two-dimensional code according to claim 11,wherein one of the plural expressions is 7-bit expression in which eightcells other than the central cell are fixed to contain four light cellsand four dark cells, the 7-bit expression representing 140 patterns. 15.The two-dimensional code according to claim 11, wherein one of theplural expressions is 6-bit expression in which eight cells other thanthe central cell are fixed to contain four light cells and four darkcells and the central cell is fixed to be light or dark, the G-bitexpression representing 70 patterns.
 16. The two-dimensional codeaccording to claim 10, wherein the plural data blocks are each dividedin such a manner to have a certain data capacity.
 17. Thetwo-dimensional code according to claim 10, wherein the data blocks eachhave a size of 3×3 cells, the separation space has a width of one ormore cells, and the position detection pattern has a lateral width offour or more cells and a vertical length of four or more cells.
 18. Amethod of analyzing the two-dimensional code according to claim 11, themethod comprising: identifying the position detection pattern;calculating the position of the format information block based on thethus identified position detection pattern; analyzing the formatinformation block to determine which of the plural expressions isrepresented by the data blocks; and performing an analysis in accordancewith the thus determined expression represented by the data blocks. 19.A storage medium for storing a program, which controls a computer toanalyze the two-dimensional code according to claim 11, wherein theprogram controls the computer such that the computer: identifies theposition detection pattern; calculates the position of the formatinformation block based on the thus identified position detectionpattern; analyzes the format information block to determine which of theplural expressions is represented by the data blocks; and performs ananalysis in accordance with the thus determined expression representedby the data blocks.
 20. A system for generating the two-dimensional codeaccording to claim 10, the system comprising: a position detectionpattern-arranging means for arranging the position detection pattern atprescribed position of a two-dimensional matrix; a dividing means fordividing, in accordance with the unit of error correction, a region ofthe two-dimensional matrix outside the region where the positiondetection pattern is arranged, into plural blocks between which aseparation space is arranged; an information block-arranging means forselecting, from the plural data blocks, information block in whichinformation required for analysis of the two-dimensional code isarranged; and a message data-arranging means for sequentially arrangingmessage-recorded data in a region of the two-dimensional matrix outsidethe regions of the position detection pattern and the information block.